Power-assisted steering device

ABSTRACT

An auxiliary power source, for example, an electric motor, supplies the power assist for a steering unit via a worm gear (15, 16). The worm gear (15, 16) drives clutch hubs (22 and 23) in the opposite rotational directions. The auxiliary power can be transferred to a driven shaft (3) via a common clamping sleeve (27) that can be expanded polygonally by two rows of clamping bodies (28 and 30) into one or the other clutch hubs (22 or 23). The clamping sleeve (27) is slitted into functional segments (A and B). Depending on the direction of rotation of the steering spindle (1), one or the other functional segments (A or B) of the clamping sleeve (27) is always active. The clutch units (2) run in a lubricant so that there is little wear and tear. This steering system can be made at reasonable cost and takes little space for installation.

This invention relates to an auxiliary power steering unit for motorvehicles consisting of a steering spindle--that can be driven by asteering hand wheel--with a steering gear. The auxiliary power acts as atorque for each turning direction, separated for one clutch unit at atime. Via reducing gears, the clutch units establish a drive connectionfrom an auxiliary drive source that rotates only in one direction to adriven shaft that drives into the steering gear.

An auxiliary power steering of the design described above is known, forexample, from DE 2746919A1. Here, an electric motor acts upon a conicalpinion via a worm wheel and a free-wheel. The conical pinion drives twoconical wheels in opposite directions and these wheels in each case areconnected to clutch drums. Furthermore, there are provided clutch cheeksthat cooperate with the clutch drums and that are connected to thesteering spindles; when a rotary movement is initiated on the manualsteering wheel which, upon initiation of a rotary movement on the manualsteering wheel, press a pair of cheeks into the clutch drum that isdriven in the same direction of rotation. In this way, one can supportthe manual rotary movement by means of the electric motor; in theprocess, the height of the support is proportional to the steeringresistance that acts upon the steered wheels.

Considerable friction value fluctuations can occur during dry-runs alongthe clutch elements that work with friction coatings, so that undercertain circumstances, the steering behavior will be influenceddifferently in the steering directions. Besides, with the lever ratiosof the clutch cheeks provided, the setting ranges are comparatively longwhich, in turn, results in a delayed response behavior. One gets acomparatively large installation space by virtue of the complicateddesign of the clutch elements radially with respect to the steeringspindle. Finally, one uses a comparatively expensive torsion bar inorder to get a softly turning connection of the two steering spindleparts.

The purpose of the invention is to find a reasonably priced,electrically supported steering system where the auxiliary force issupplied uniformly without delay as a function of the supplied manualforce. Another requirement is to house the steering system also in tightspaces.

The invention consists in the fact that clamping bodies guided in acommon cage and acting in both directions of rotation are provided andthat the clamping bodies act upon a common clamping sleeve that issubdivided into functional segments and that is slitted. The clampingsleeve rests with a small interval inside two clutch hubs that aredriven in different directions of rotation by the reducing gear. Theclutch unit gear works in such a way that--in case of a steeringmovement--as a function of the steering torque on the manual steeringwheel, there will--by virtue of the clamping body--be a polygonalspreading of one of the two functional segments of the clamping sleeveagainst one or the other clutch hub. This spreading can be achieved bymeans of clamping slopes on the inside diameter of the clamping sleeveon which the clamping bodies run up. The clamping sleeve transmits theauxiliary torque, for example, of an electric motor upon the drivenshaft in both directions of rotation.

The steering unit according to the invention works with small settingranges so that the auxiliary torque can, without response delay, be fedinto the driven [shaft] portion of the steering spindle. One getsuniform friction forces with minimum wear and tear because the clutchunit runs in a lubricating agent. Moreover, by means of the space-savingdesign of the clutch elements, one can achieve a rather cramped outershape so that the steering system can also be used in smaller vehicles.

The invention is not confined to the combinations of features given inthe claims. The experts will find additional meaningful possibilities ofcombining claims and individual claim features from the problemstatement.

The invention will now be explained in greater detail with the help ofthe drawing showing practical examples.

FIG. 1 is a longitudinal profile through an electrical auxiliary powersteering [unit] with manual selection [drive] where the auxiliary unitis integrated into the steering [unit];

FIG. 2 is a reduced-size lateral profile along line II--II in FIG. 1;

FIG. 3 is a reduced-size lateral profile along line III--III in FIG. 2;

FIG. 4 is an enlarged partial profile in which the clutch units aredrawn for left-hand and right-hand driving in an imaginary commondrawing plane in the straight-ahead running position;

FIG. 5 is an enlarged partial profile of one of the clutch unitscorresponding to FIG. 2 when steering to the left;

FIG. 6 is an enlarged partial profile of the other clutch unitcorresponding to line VI--VI in FIG. 1 when steering to the right;

FIGS. 7 to 10 show various models of the clamping sleeve in partialdeveloped views;

FIG. 11 is another model of a clutch unit;

FIG. 12 shows a partial developed view of the clamping sleeve belongingto the clutch unit according to FIG. 11;

FIG. 13 is a version of a clutch unit with only one row of clutchbodies;

FIG. 14 is a partial developed view of the pertinent clamping sleeve;

FIG. 15 is another version shown in a partial profile according to FIG.4, but with additional axial bars along the friction surface of theclamping sleeve;

FIG. 16 shows the electric motion attached to the worm gear by a cardanshaft; and

FIG. 17 shows the electric motor attached to the worm gear by a flexibledraft.

The basic idea behind the invention is--by means of clamping bodiesgrouped around the steering spindle--depending on the direction ofrotation, to couple two mutually independent clutch hubs with a clampingsleeve which works in both directions of rotation. The clamping sleeve,in other words, establishes a connection via the clutch hubs from adrive source that supplies the auxiliary power to the steering gear.

In FIG. 1, a steering spindle 1 connected with a manual steering wheelnot shown in the drawing is connected via clutch units 2 with a drivenshaft 3. Driven shaft 3 is a part of a steering gear 4--in thisparticular case, a steering rack gear consisting of a pinion 5, asteering rack 6, and a press-on device 7. A spring 8 sits betweensteering spindle 1 and driven shaft 3 for axial play equalization. Theaxial forces can thus be absorbed in roller bearings 10 and 11 thatsimultaneously radially support pinion 5 or steering spindle 1. Anotherradial roller bearing 19 supports the driven shaft 3 that is firmlyconnected with pinion 5 and the steering spindle 1 that is positioned ondriven shaft 3. In a thickened portion of steering spindle 1, there arerecesses 9 that engage catches on driven shaft 3 with a certain twistingplay. Spring 8 allows this kind of twisting or steering play, but in theprocess, it is slightly twisted within itself.

According to FIGS. 2 and 3, a drive source that supplies the auxiliarypower--for example, an electric motor 12--via a spur pinion pair 13 and14 drives two worm gears 15 and 16 in a counter-rotating manner. Eachworm gear consists of a pinion 17 or 18 that engages a wheel 20 or 21.Each wheel 20 and 21 is connected with a clutch hub 22 or 23 (FIG. 1).Clutch hubs 22 and 23 are supported on oblique bearings 24 and 25.Between the two clutch hubs 22 and there is a so-called expansionbearing 26 that provides for the clutch hubs to come to rest axially inthe oblique bearings 24 and 25 without any play. The clutch units thatare separated for each direction of steering, in addition to clutch hubs22 and 23, consist of a clamping sleeve 27 that is subdivided into twofunctional segments A and B, two rows of clamping bodies 28 and 30, acommon cage 31, as well as several running surfaces 32 for the clampingbodies (FIGS. 5 to 7). In the practical example at hand, the thickenedpart of steering spindle 1 has a hexagonal profile whose surfaces areused as running surfaces 32. Clamping bodies 28 and 30 are held in acommon cage 31. Clamping sleeve 27 grasps the two rows of clampingbodies 28 and 30 in a bell-shaped manner. A play "S" (FIG. 4) remainsbetween clamping sleeve 27 and the two clutch hubs 22 and 23. Clampingsleeve 27 is practicably attached to the driven shaft 3 by means of agroove toothing 34. Clamping sleeve 27 can also be made as a cylindricalcomponent without the bell-like attachment. In this case, one provides acorrespondingly large collar on driven shaft 3 that can beflange-mounted on the cylindrical component (clamping sleeve 27).

The functional segments A and B of the clamping sleeve 27 have clampingslopes 35 and 36 that are attached in opposite directions. Theinclination angle of the clamping slopes 35 with the pertinent clampingbodies 28 can be seen in FIG. 5 for a steering deflection to the leftand the inclination angle of the clamping slopes for clamping bodies 30can be seen from FIG. 6 for a steering deflection to the right.

If one fills an installation space of the clutch devices 2 with alubricant, then one gets a low-wear force transmission. As one can seein FIG. 1, it is advantageous to work lubricating grooves 38 or 39 intothe clutch hubs 22 and 23 in the area of functional segments A and B ofthe clamping sleeve 27. These lubricating grooves take care of a rapiddisplacement of the existing lubricating agent wedge. In this way, onegets a higher friction value and the auxiliary torque is supplieduniformly.

FIG. 7 shows the clamping sleeve 27 according to FIG. 1 in the developedview. Distributed over the circumference, clamping sleeve 27 has threerows of slits 40, 41 and 42. Slits 40 and 41 lie on the same levelwhereas slits 42 are arranged staggered with respect to theabove-mentioned slits. Slits 40 and 41 enclose functional segment Abetween them, whereas slits 42 and an outer rim 37 of the clampingsleeve form the functional segment B. There is a neutral zone C betweenthe two closely adjacent slits 41 and 42. Slit rows 40, 41 and 42 are sopositioned with respect to each other that the functional segments A andB are uncoupled from each other in a radial direction by a polygonaldeformation although they are rigidly connected with each other in thecircumferential, direction. Clamping bodies 28 lie in the middle ofslits 40 and 41 and clamping bodies 30 lie staggered with respect toclamping bodies 28 between slits 42 and rim 37. Clamping bodies 28 and30 run in the inside diameter of clamping sleeve 27 in the correspondingclamping slopes 35 or 36.

The auxiliary power steering unit works as follows:

FIG. 4 shows the position for straight-ahead running. Here, clampingbodies 28 and 30--which are illustrated in the same plane ofdrawing--are in their neutral middle position. Clamping sleeve 27 heremaintains the play labeled "S" along its entire circumference withrespect to the two clutch hubs 22 and 23. Accordingly, there cannot be apower transmission from clamping sleeve 27 to one of the two clutch hubs22 or 23.

If the driver supplies a torque into the steering spindle 1 by turningto the left on the manual steering wheel according to FIG. 5, then therunning surfaces 32 of steering spindle 1 will be pointing in thedirection of the arrow. Clamping bodies 28 are pressed into clampingslopes 35 covering a steering path [distance] "W." The functionalsection of clamping sleeve 27 that is labeled A here spreads over theclamping body 28. In the process, clamping sleeve 27 is pressed into theclutch hub 22 that is driven in the corresponding direction of rotationby electric motor 12. The auxiliary power can thus be supplied viaclamping sleeve 27 into driven shaft 3 and via steering gear 4 into thesteered wheels. In this process, one must keep in mind that onlyfunctional segment A of clamping sleeve 27 is active. From neutral zoneC onward, there is no further deformation; instead, the latter gets itsplay "S" with relation to clutch hub 23 on account of the specialarrangement of slits 40, 41, 42. If the driver no longer exerts anysteering force, then clamping bodies 28 roll back into their middleposition (FIG. 4), that is to say, the steering again moves in theneutral position. Clamping bodies 28 thus assume the function of anotherwise customary torsion bar.

When the manual steering wheel is turned to the right, clamping sleeve27 is polygonally expanded in its functional segment B into the clutchhub 23 by virtue of the active clamping bodies 30; this can be seen ingreater detail in FIG. 6. Because the worm gear 16 drives clutch hub 23in the opposite direction, clamping sleeve 27 together with drive shaft3 will turn in the direction indicated by the arrows.

If electric motor 12 should fail due to trouble, it can be uncoupledfrom the steering train with the help of a free-wheel that is notvisible. In that case, the driver must not turn the electric motor alongwith a steering motion with any increased force expenditure. The entiretorque is transmitted from the steering spindle 1 to driven shaft 3after overcoming the twisting play created by catches 9.

The version of a clamping sleeve 43 according to FIG. 8 shows two rowsof slits 44 and 45 that are distributed over the circumference and thatare staggered with each other and that are directed axially and thatagain form functional segments A and B. Here, clamping bodies 46 and 47lie in the extension to slits 44 and 45.

In another design of a clamping sleeve 48 according to FIG. 9, U-shapedslits 50 and L-shaped slits 52, whose short legs 51 point outward, areassociated with functional segments A and B. Clamping bodies 53 offunctional segment A lie within the U-shape and clamping bodies 54 offunctional segment B lie inside the L-shape.

In another version according to FIG. 10, one uses a clamping sleeve 49with two rows of slits 55 and 56 that are aligned with respect to eachother in the circumferential direction. Here, clamping bodies 57 offunctional segment A lie between every other pair of slits 55 and 56that are aligned toward each other. Here, connecting bars 65 and 66 liebetween functional segments A and B in a neutral widening zone, that isto say, in the area in which clamping sleeve 49 is not radiallydeformed.

Clamping bodies 58 of functional segment B lie, staggered with respectto clamping bodies 57, between one rim of clamping sleeve 49 and the rowof slits 56 that roughly lies in the middle.

The design according to FIGS. 11 and 12 shows clamping bodies 60 and 61in the shape of crowned clamping plates. These clamping bodies 60, 61are supported between two common grooves 63 of the steering spindle andimpressions 62 on the inside of clamping sleeve 64. Clamping bodies 60or 61 are positioned obliquely against their particular direction ofaction and are erected during steering. In the process, clamping sleeve27 as in the previously discussed versions is tightened in theassociated clutch hub in a point-shaped manner. Naturally, it is alsopossible to change the bracing support for clamping bodies 60 and 61 insuch a way that grooves 63 will lie in clamping sleeve 64 and that theimpressions will lie in the steering spindle,

FIGS. 13 and 14 finally shows a version with a clamping sleeve 70 thatin its two functional segments A and B reveals clamping slopes 67 or 68that are inclined opposite to each other. These clamping slopes 67 and68 cooperate only with one row of clamping bodies 71 that however reveala greater length and that thus reveal two working areas whose functionis separated. One can omit the cage here. Depending on the direction ofrotation, one of the two working areas activates functional segment A orfunctional segment B of clamping sleeve 70.

To increase the resistance to wear and tear, one can coat the frictionsurfaces of clutch hubs 22 and 23 with a wear-resistant material. Thefriction surfaces, for example, can be nitrocarbonated or can beprovided with a molybdenum coating.

If the installation conditions are particularly tight when the auxiliarypower steering unit is built in, for example, in small cars, thenelectric motor 12 can be separated from the remaining structural unit(worm gears 16, clutch units 2, steering gear 4). Electric motor 12, forexample, can be attached under the windshield along the splashboard orin a wheel housing and connection to the worm gear 16 can be establishedby a cardan shaft 75, as shown in FIG. 16 or a flexible shaft 76, asshown in FIG. 17.

It is within the context of the invention to build in a structural unitconsisting of worm gear 16 and clutch devices 2 immediately under themanual steering wheel and to establish connection to steering gear 4 viaa prolonged driven shaft 3.

Another version according to FIG. 15 shows a clamping sleeve 69 withslits and associated roller bodies according to any of FIGS. 7 to 10 or12. One essential difference, however, consists in the fact that thefriction surface is provided with narrow, axially extending bars 70 or71 in the area of the roll bodies. Depending on the steering direction,bars 70 or 71 will rest in corresponding functional segment A or B inthe clutch hub 20 or 23 (FIG. 1). For reasons of production, bars 70 and71 extend over the entire width of clamping sleeve 69. These bars havethe property that they easily penetrate through the lubricant film andtherefore facilitate temperature-independent power transmission.

By way of overload safety, the electric motor advantageously gets atemperature sensor that interrupts the power supply in case of excessiveheating.

For reasons of energy savings, it is furthermore practical to turn theelectric motor on only as of a certain low driving speed (for example,v=<10 km/hr) so that the steering force support will take effect only athigher steering forces.

    ______________________________________                                        Reference Symbols                                                             ______________________________________                                                 1   Steering spindle                                                          2   Clutch unit                                                               3   Driven shaft                                                              4   Steering gear                                                             5   Pinion                                                                    6   Rack                                                                      7   Press-on device                                                           8   Spring                                                                    9   Catch                                                                     10  Roller bearing                                                            11  Roller bearing                                                            12  Electric motor                                                            13  Spur wheel                                                                14  Spur wheel                                                                15  Worm gear                                                                 16  Worm gear                                                                 17  Pinion                                                                    18  Pinion                                                                    19  Radial roller bearing                                                     20  Wheel                                                                     21  Wheel                                                                     22  Clutch hub                                                                23  Clutch hub                                                                24  Oblique bearing                                                           25  Oblique bearing                                                           26  Expansion bearing                                                         27  Clamping sleeve                                                           28  Clamping body                                                             29  --                                                                        30  Clamping body                                                             31  Cage                                                                      32  Running surface                                                           33  --                                                                        34  Groove toothing                                                           35  Clamping slope                                                            36  Clamping slope                                                            37  Rim of 27                                                                 38  Lubricating grooves                                                       39  Lubricating grooves                                                       40  Slits                                                                     41  Slits                                                                     42  Slits                                                                     43  Clamping sleeve                                                           44  Slits                                                                     45  Slits                                                                     46  Clamping body                                                             47  Clamping body                                                             48  Clamping sleeve                                                           49  Clamping sleeve                                                           50  U-shaped slits                                                            51  Short legs                                                                52  L-shaped slits                                                            53  Clamping body                                                             54  Clamping body                                                             55  Slits                                                                     56  Slits                                                                     57  Clamping body                                                             58  Clamping body                                                             59  --                                                                        60  Clamping body (plates)                                                    61  Clamping body                                                             62  Impressions                                                               63  Grooves                                                                   64  Clamping sleeve                                                           65  Connecting bar                                                            66  Connecting bar                                                            67  Clamping slope                                                            68  Clamping slope                                                            69  Clamping sleeve                                                           70  Bar                                                                       71  Bar                                                              ______________________________________                                    

We claim:
 1. An auxiliary power steering unit for a motor vehiclecomprising:a polygonal steering spindle (1) which is driven in rotationin both directions by a manual steering wheel of the vehicle; a steeringgear (4); a driven shaft (3) which connects said steering spindle tosaid steering gear; an auxiliary drive source (12) which produces atorque, said drive source including first and second reducing gears (15,16) which provide a torque for each direction of rotation of saidsteering spindle; and first and second clutch units (2) which establisha respective drive connection from a respective said reducing gear tosaid driven shaft, said clutch units includinga common cage (31) forboth respective said clutch units which is located radially about saidpolygonal steering spindle, first and second clamping bodies (28, 30)which are guided by said cage for rotation in both directions by contactwith said polygonal steering spindle, a slitted clamping sleeve (27)which is divided into first and second functional segments (A, B) whichsaid functional segments are respectively engaged with a respective oneof said first and second clamping bodies (28, 30), and first and secondclutch hubs (22, 23) within which said clamping sleeve is disposed witha gap (5) therebetween, said clutch hubs being oppositely driven inrotation by a respective one of said reducing gears whereby upon asteering movement of said polygonal steering spindle a respective one ofsaid clamping bodies (28, 30) is moved radially to engage an associatedfunctional segment (A, B) of said clamping sleeve (27) with anassociated said clutch hub (22, 23) so that said clamping sleeve iscorrespondingly driven in rotation by said drive source thereby drivingsaid driven shaft (3).
 2. An auxiliary power steering unit as claimed inclaim 1wherein said clamping sleeve (27) and has three rows of slits(40, 41, 42) thereabout; wherein there is a row of said first clampingbodies (28) and a row of said second clamping bodies (30),each of saidrows of said clamping bodies working independently from one another,each said first and second clamping body of a respective said first andsecond row working together while engaging said polygonal steeringspindle so as to be all moved radially by movement of said steeringspindle; and wherein said slitted clamping sleeve (27) is a unitaryelement and includesfirst and second rows of slits (40, 41) which extendin a circumferential direction, in which said slits of each said row arealigned parallel and adjacent one another, and in which said first andsecond rows of slits are arranged with said first row of said firstclamping bodies associated with said first functional segment (A)therebetween, a third row of slits (42) which extend in acircumferential direction, which are located between an outer rim (37)of said clamping sleeve (27) and an adjacent one of said first andsecond rows of slits, which has said slits of said third row paralleland staggered with respect to said slits of the adjacent one of saidfirst and second rows of slits, and which is located with said secondrow of clamping bodies (30) associated with said second functionalsegment (B) between said third row of slits (42) and said outer rim(37), and respective first and second slopes (35, 36) which lie along aninside diameter of respective said first and second functional segments(A, B) of said clamping sleeve (27) and in between which said first andsecond slopes respective said first and second clamping bodies aredisposed, said first and second slopes having inclination angles inopposite directions.
 3. An auxiliary power steering unit as claimed inclaim 2 wherein said row of said first clamping bodies (28) associatedwith said first functional segment (A) lie axially centered adjacentrespective said slits of said first and second rows of slits (40, 41),and wherein said row of said second clamping bodies (30) associated withsaid second functional segment (B) lie axially centered adjacentrespective said slits of said third row of slits (42).
 4. An auxiliarypower steering unit as claimed in claim 1 wherein said clamping sleeve(27) is bell shaped having a narrow end which engages about said drivenshaft (3) with mutual grooved teeth and a wide end which extends aboutsaid steering spindle (1).
 5. An auxiliary power steering unit asclaimed in claim 1 wherein said clamping sleeve (27) includes first andsecond rows of slits (44, 45) which extend axially inward from oppositesides of said sleeve (27) and which are staggered with respect to oneanother, and wherein there are a plurality of said first and secondclamping bodies (46,47) which are respectively located axially adjacentinward ends of respective said slits of said first and second rows ofslits (44, 45).
 6. An auxiliary power steering unit as claimed in claim1 wherein said first functional segment (A) of said clamping sleeve (48)includes U-shaped slits (50) having opposed legs extending in acircumferential direction and a plurality of said first clamping bodies(53) are respectively located between respective said opposed legs; andwherein said second functional segment (B) of said clamping sleeve (48)includes L-shaped slits (51) having short legs extending in an axialdirection from a rim of said clamping sleeve (48) and a plurality ofsaid second clamping bodies (54) are respectively located betweenrespective said short legs and said rim.
 7. An auxiliary power steeringunit as claimed in claim 1 wherein said clamping sleeve (49) includesanouter rim; and first and second rows of slits (55, 56) which extend in acircumferential direction parallel to one another and with said slits ofeach row opposite one another, a plurality of said first clamping bodies(57) being respectively arranged circumferentially between every otheropposed pair of slits (55, 56) and a plurality of said second clampingbodies (58) being respectively arranged between said rim and theadjacent said row of slits and staggered with respect to adjacent saidfirst clamping bodies.
 8. An auxiliary power steering unit as claimed inclaim 1wherein said clamping bodies (60, 61) are formed as crownedclamping plates; wherein said steering spindle (1) includes two commongrooves (63) in which said crowned clamping plates are supported; andwherein said clamping sleeve (64) includes impressions (62) in whichsaid crowned clamping plates are obliquely received relative to arespective direction of action.
 9. An auxiliary power steering unit asclaimed in claim 1wherein said clamping sleeve (70) includes first andsecond clamping slopes (67, 68) which are circumferentially oppositelydirected and which are located in respective functional segments (A, B);and wherein said first and second clamping bodies are formed as aunitary roller (71) which engages both said first and second clampingslopes.
 10. An auxiliary power steering unit as claimed in claim 1 andfurther including a lubricant in which said clutch units (2) run.
 11. Anauxiliary power steering unit as claimed in claim 1 wherein said clutchunits further include oblique bearings (24, 25) which position saidclutch hubs (22, 23) for rotation and an expansion bearing (26) whicheliminates any axial play between said clutch hubs.
 12. An auxiliarypower steering unit as claimed in claim 1 wherein said auxiliary drivesource is an electric motor (12) which is housed separately from saidclutch units (2) and which includes a worm gear (16) adjacent saidclutch units and a cardan shaft (75) connecting said electric motor andsaid worm gear.
 13. An auxiliary power steering unit as claimed in claim1 wherein said auxiliary drive source is an electric motor (12) which ishoused separately from said clutch units (2) and which includes a wormgear (16) adjacent said clutch units and a flexible shaft (76)connecting said electric motor and said worm gear.
 14. An auxiliarypower steering unit as claimed in claim 1 and further including rollerbearings (10, 11) in which said steering spindle (1) and said drivenshaft (3) are mounted for rotation and a spring (8) positioned betweensaid steering spindle (1) and said driven shaft (8) to eliminate axialplay therebetween.
 15. An auxiliary power steering unit as claimed inclaim 1 and further including lubricating grooves (38, 39) provided in aface of said clutch hubs (22, 23) adjacent said clamping sleeve (27).16. An auxiliary power steering unit as claimed in claim 1 wherein saidclutch hubs (22, 23) include a friction surface adjacent said clampingsleeve (27) which is coated with a wear-resistant material.
 17. Anauxiliary power steering unit as claimed in claim 1 wherein saidclamping sleeve (69) includes axial bars (70, 71) on an outside surfacethereof opposite to said clamping bodies (28, 30).